Best way, use a knife and slice it thiin.
Then just place it on the bread.
If the bread is the slightest bit warm (why would you eat cold bread !?), it melts right away.
But of course, for that to work, you need to be offered the larger face of the butter instead of the little side, that people tend to slice.
I tend to apply it on toast (i.e. toasted, sliced bread) in that way, which I toasted with a few drops of groundnut oil or Ghee, and it melts (enough to spread by just touching and dragging the spoon/knife) by the time I am ready to eat.